Laser cutting system and methods for creating self-retaining sutures

ABSTRACT

A laser-machining system and method is disclosed for forming retainers on a suture thread. The laser system is preferably a femtosecond laser system which is capable of creating submicron features on the suture thread while preserving strength of the suture thread. The laser-machining system enables creation of retainers and self-retaining suture systems in configurations which are difficult and/or impossible to achieve using mechanical cutting technology.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application under 35 U.S.C. 371 of PCT/US2011/035270, filed on May 4, 2011, which claims priority from U.S. Provisional Application Ser. No. 61/331,294, filed on May 4, 2010 and U.S. Provisional Application Ser. No. 61/331,302, filed on May 4, 2010.

FIELD OF INVENTION

The present invention relates generally to laser-cutting equipment and methods of manufacturing self-retaining suture systems for surgical procedures.

BACKGROUND OF INVENTION

Wound closure devices such as sutures, staples and tacks have been widely used in superficial and deep surgical procedures in humans and animals for closing wounds, repairing traumatic injuries or defects, joining tissues together (bringing severed tissues into approximation, closing an anatomical space, affixing single or multiple tissue layers together, creating an anastomosis between two hollow/luminal structures, adjoining tissues, attaching or reattaching tissues to their proper anatomical location), attaching foreign elements to tissues (affixing medical implants, devices, prostheses and other functional or supportive devices), and for repositioning tissues to new anatomical locations (repairs, tissue elevations, tissue grafting and related procedures) to name but a few examples.

Sutures are often used as wound closure devices. Sutures typically consist of a filamentous suture thread attached to a needle with a sharp point. Suture threads can be made from a wide variety of materials including bioabsorbable (i.e., that break down completely in the body over time), or non-absorbable (permanent; non-degradable) materials. Absorbable sutures have been found to be particularly useful in situations where suture removal might jeopardize the repair or where the natural healing process renders the support provided by the suture material unnecessary after wound healing has been completed; as in, for example, completing an uncomplicated skin closure. Non-degradable (non-absorbable) sutures are used in wounds where healing may be expected to be protracted or where the suture material is needed to provide physical support to the wound for long periods of time; as in, for example, deep tissue repairs, high tension wounds, many orthopedic repairs and some types of surgical anastomosis. Also, a wide variety of surgical needles are available; the shape and size of the needle body and the configuration of the needle tip is typically selected based upon the needs of the particular application.

To use an ordinary suture, the suture needle is advanced through the desired tissue on one side of the wound and then through the adjacent side of the wound. The suture is then formed into a “loop” which is completed by tying a knot in the suture to hold the wound closed. Knot tying takes time and causes a range of complications, including, but not limited to (i) spitting (a condition where the suture, usually a knot) pushes through the skin after a subcutaneous closure), (ii) infection (bacteria are often able to attach and grow in the spaces created by a knot), (iii) bulk/mass (a significant amount of suture material left in a wound is the portion that comprises the knot), (iv) slippage (knots can slip or come untied), and (v) irritation (knots serve as a bulk “foreign body” in a wound). Suture loops associated with knot tying may lead to ischemia (knots can create tension points that can strangulate tissue and limit blood flow to the region) and increased risk of dehiscence or rupture at the surgical wound. Knot tying is also labor intensive and can comprise a significant percentage of the time spent closing a surgical wound. Additional operative procedure time is not only bad for the patient (complication rates rise with time spent under anesthesia), but it also adds to the overall cost of the operation (many surgical procedures are estimated to cost between $15 and $30 per minute of operating time).

Self-retaining sutures (including barbed sutures) differ from conventional sutures in that self-retaining sutures possess numerous tissue retainers (such as barbs) which anchor the self-retaining suture into the tissue following deployment and resist movement of the suture in a direction opposite to that in which the retainers face, thereby eliminating the need to tie knots to affix adjacent tissues together (a “knotless” closure). Knotless tissue-approximating devices having barbs have been previously described in, for example, U.S. Pat. No. 5,374,268, disclosing armed anchors having barb-like projections, while suture assemblies having barbed lateral members have been described in U.S. Pat. Nos. 5,584,859 and 6,264,675. Sutures having a plurality of barbs positioned along a greater portion of the suture are described in U.S. Pat No. 5,931,855, which discloses a unidirectional barbed suture, and U.S. Pat. No. 6,241,747, which discloses a bidirectional barbed suture. Methods and apparatus for forming barbs on sutures have been described in, for example, U.S. Pat. No. 6,848,152. Self-retaining systems for wound closure also result in better approximation of the wound edges, evenly distribute the tension along the length of the wound (reducing areas of tension that can break or lead to ischemia), decrease the bulk of suture material remaining in the wound (by eliminating knots) and reduce spitting (the extrusion of suture material—typically knots—through the surface of the skin. All of these features are thought to reduce scarring, improve cosmesis, and increase wound strength relative to wound closures using plain sutures or staples. Thus, self-retaining sutures, because such sutures avoid knot tying, allow patients to experience an improved clinical outcome, and also save time and costs associated with extended surgeries and follow-up treatments. It is noted that all patents, patent applications and patent publications identified throughout are incorporated herein by reference in their entirety.

The ability of self-retaining sutures to anchor and hold tissues in place even in the absence of tension applied to the suture by a knot is a feature that also provides superiority over plain sutures. When closing a wound that is under tension, this advantage manifests itself in several ways: (i) self-retaining sutures have a multiplicity of retainers which can dissipate tension along the entire length of the suture (providing hundreds of “anchor” points this produces a superior cosmetic result and lessens the chance that the suture will “slip” or pull through) as opposed to knotted interrupted sutures which concentrate the tension at discrete points; (ii) complicated wound geometries can be closed (circles, arcs, jagged edges) in a uniform manner with more precision and accuracy than can be achieved with interrupted sutures; (iii) self-retaining sutures eliminate the need for a “third hand” which is often required for maintaining tension across the wound during traditional suturing and knot tying (to prevent “slippage” when tension is momentarily released during tying); (iv) self-retaining sutures are superior in procedures where knot tying is technically difficult, such as in deep wounds or laparoscopic/endoscopic procedures; and (v) self-retaining sutures can be used to approximate and hold the wound prior to definitive closure. As a result, self-retaining sutures provide easier handling in anatomically tight or deep places (such as the pelvis, abdomen and thorax) and make it easier to approximate tissues in laparoscopic/endoscopic and minimally invasive procedures; all without having to secure the closure via a knot. Greater accuracy allows self-retaining sutures to be used for more complex closures (such as those with diameter mismatches, larger defects or purse string suturing) than can be accomplished with plain sutures.

A self-retaining suture may be unidirectional, having one or more retainers oriented in one direction along the length of the suture thread; or bidirectional, typically having one or more retainers oriented in one direction along a portion of the thread, followed by one or more retainers oriented in another (often opposite) direction over a different portion of the thread (as described with barbed retainers in U.S. Pat. Nos. 5,931,855 and 6,241,747). Although any number of sequential or intermittent configurations of retainers are possible, one form of unidirectional self-retaining suture includes a tissue anchor on the distal end and a needle on the proximal end and a plurality of barbs on the surface of the suture thread having tips projecting “away” from the needle. Projecting “away” from the needle means that the tip of the barb is further away from the needle and the portion of suture comprising the barb may be pulled more easily through tissue in the direction of the needle than in the opposite direction (towards the tissue anchor). The tissue anchor is designed to secure the distal end of the suture and includes in some embodiments a loop, staple, tack, bar, plug, sheet, or ball.

Although any number of sequential or intermittent configurations of retainers are possible, one form of bidirectional self-retaining suture includes a needle at one end of a suture thread which has barbs having tips projecting “away” from the needle until the transition point (often the midpoint) of the suture is reached; at the transition point the configuration of barbs reverses itself about 180° (such that the barbs are now facing in the opposite direction) along the remaining length of the suture thread before attaching to a second needle at the opposite end (with the result that the barbs on this portion of the suture also have tips projecting “away” from the nearest needle). Put another way, the barbs on both “halves” of a typical bidirectional self-retaining suture have tips that point towards the middle, with a transition segment (lacking barbs) interspersed between them, and with a needle attached to either end.

SUMMARY OF INVENTION

Despite the multitude of advantages of unidirectional and bidirectional self-retaining sutures, there remains a need to improve upon the design of the suture such that a variety of limitations can be eliminated and enhanced and/or additional functionality is provided.

In accordance one aspect, the present invention provides laser cutting apparatus for creating retainers on a suture thread.

In accordance with another aspect, the present invention provides apparatus for stabilizing a suture during laser-cutting of retainers.

In accordance with another aspect, the present invention provides methods for cutting retainers on a suture thread with a laser.

The details of one or more embodiments are set forth in the description below. Other features, objects and advantages will be apparent from the description, the drawings, and the claims. In addition, the disclosures of all patents and patent applications referenced herein are incorporated by reference in their entirety. For example, this application incorporates by reference U.S. application Ser. No. ______, filed ______, (Attorney Reference No. 2284.40854USPC), which is the U.S. National Phase of International Application No. ______ filed May 4, 2011, entitled SELF-RETAINING SYSTEM HAVING LASER-CUT RETAINERS (Attorney Reference No. 2284.40854PC).

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the invention, its nature and various advantages will be apparent from the accompanying drawings and the following detailed description of various embodiments.

FIG. 1A is a perspective view of a bidirectional self-retaining suture.

FIGS. 1B-1D are enlarged views of portions of the suture of FIG. 1A.

FIG. 1E is a perspective view of a unidirectional self-retaining suture.

FIGS. 1F-1H are views of alternative tissue anchors for the unidirectional self-retaining suture of FIG. 1E.

FIG. 2A shows a schematic diagram of a laser-machining system suitable for forming retainers on a suture thread according to an embodiment of the present invention.

FIG. 2B is an image of a Gaussian laser beam.

FIG. 2C is a graphical representation of the power density distribution in a Gaussian laser beam.

FIG. 2D is an image of a laser beam from an axicon prism system.

FIG. 2E is a graphical representation of the power density distribution in a laser beam from an axicon prism system.

FIG. 3A shows a sectional view of an air bearing for use in the laser-machining system of FIG. 2 according to an embodiment of the present invention.

FIG. 3B shows a partial perspective view of the air bearing of FIG. 3A.

FIG. 4A is a flow chart of a method for creating a self-retaining suture utilizing the laser-machining system of FIG. 2 according to an embodiment of the present invention.

FIGS. 4B-4D are perspective views of a suture filament during the process of generating a laser-cut retainer utilizing the laser-machining system of FIG. 2 according to an embodiment of the present invention.

FIG. 5 is an image of a laser-cut surface of a self-retaining suture.

FIG. 6 is a graph showing the profile of the laser-cut surface of FIG. 5.

FIG. 7 shows a retainer distribution configurations for a self-retaining suture made utilizing the laser-machining system of FIG. 2.

FIGS. 8A-8F show examples of self-retaining sutures made utilizing the laser-machining system of FIG. 2.

DETAILED DESCRIPTION Definitions

Definitions of certain terms that may be used hereinafter include the following.

“Self-retaining system” refers to a self-retaining suture together with devices for deploying the suture into tissue. Such deployment devices include, without limitation, suture needles and other deployment devices as well as sufficiently rigid and sharp ends on the suture itself to penetrate tissue.

“Self-retaining suture” refers to a suture that comprises features on the suture filament for engaging tissue without the need for a knot or suture anchor.

“Tissue retainer” (or simply “retainer”) or “barb” refers to a physical feature of a suture filament which is adapted to mechanically engage tissue and resist movement of the suture in at least one axial directions. By way of example only, tissue retainer or retainers can include hooks, projections, barbs, darts, extensions, bulges, anchors, protuberances, spurs, bumps, points, cogs, tissue engagers, traction devices, surface roughness, surface irregularities, surface defects, edges, facets and the like. In certain configurations, tissue retainers are adapted to engage tissue to resist movement of the suture in a direction other than the direction in which the suture is deployed into the tissue by the physician, by being oriented to substantially face the deployment direction. In some embodiments the retainers lie flat when pulled in the deployment direction and open or “fan out” when pulled in a direction contrary to the deployment direction. As the tissue-penetrating end of each retainer faces away from the deployment direction when moving through tissue during deployment, the tissue retainers should not catch or grab tissue during this phase. Once the self-retaining suture has been deployed, a force exerted in another direction (often substantially opposite to the deployment direction) causes the retainers to be displaced from the deployment position (i.e. resting substantially along the suture body), forces the retainer ends to open (or “fan out”) from the suture body in a manner that catches and penetrates into the surrounding tissue, and results in tissue being caught between the retainer and the suture body; thereby “anchoring” or affixing the self-retaining suture in place. In certain other embodiments, the tissue retainers may be configured to permit motion of the suture in one direction and resist movement of the suture in another direction without fanning out or deploying. In certain other configurations, the tissue retainer may be configured or combined with other tissue retainers to resist motion of the suture filament in both directions. Typically a suture having such retainers is deployed through a device such as a cannula which prevents contact between the retainers and the tissue until the suture is in the desired location.

“Retainer configurations” refers to configurations of tissue retainers and can include features such as size, shape, flexibility, surface characteristics, and so forth. These are sometimes also referred to as “barb configurations”.

“Bidirectional suture” refers to a self-retaining suture having retainers oriented in one direction at one end and retainers oriented in the other direction at the other end. A bidirectional suture is typically armed with a needle at each end of the suture thread. Many bidirectional sutures have a transition segment located between the two barb orientations.

“Transition segment” refers to a retainer-free (barb-free) portion of a bidirectional suture located between a first set of retainers (barbs) oriented in one direction and a second set of retainers (barbs) oriented in another direction. The transition segment can be at about the midpoint of the self-retaining suture, or closer to one end of the self-retaining suture to form an asymmetrical self-retaining suture system.

“Suture thread” refers to the filamentary body component of the suture. The suture thread may be a monofilament, or comprise multiple filaments as in a braided suture. The suture thread may be made of any suitable biocompatible material, and may be further treated with any suitable biocompatible material, whether to enhance the sutures' strength, resilience, longevity, or other qualities, or to equip the sutures to fulfill additional functions besides joining tissues together, repositioning tissues, or attaching foreign elements to tissues.

“Monofilament suture” refers to a suture comprising a monofilamentary suture thread.

“Braided suture” refers to a suture comprising a multifilamentary suture thread. The filaments in such suture threads are typically braided, twisted, or woven together.

“Degradable suture” (also referred to as “biodegradable suture” or “absorbable suture”) refers to a suture which, after introduction into a tissue is broken down and absorbed by the body. Typically, the degradation process is at least partially mediated by, or performed in, a biological system. “Degradation” refers to a chain scission process by which a polymer chain is cleaved into oligomers and monomers. Chain scission may occur through various mechanisms, including, for example, by chemical reaction (e.g., hydrolysis, oxidation/reduction, enzymatic mechanisms or a combination of these) or by a thermal or photolytic process. Polymer degradation may be characterized, for example, using gel permeation chromatography (GPC), which monitors the polymer molecular mass changes during erosion and breakdown. Degradable suture material may include polymers such as polyglycolic acid, copolymers of glycolide and lactide, copolymers of trimethylene carbonate and glycolide with diethylene glycol (e.g., MAXON™, Covidien), terpolymer composed of glycolide, trimethylene carbonate, and dioxanone (e.g., BIOSYN™ [glycolide (60%), trimethylene carbonate (26%), and dioxanone (14%)], Covidien), copolymers of glycolide, caprolactone, trimethylene carbonate, and lactide (e.g., CAPROSYN™ Covidien). A dissolvable suture can also include partially deacetylated polyvinyl alcohol. Polymers suitable for use in degradable sutures can be linear polymers, branched polymers or multi-axial polymers. Examples of multi-axial polymers used in sutures are described in U.S. Patent Application Publication Nos. 2002/0161168, 2004/0024169, and 2004/0116620. Sutures made from degradable suture material lose tensile strength as the material degrades. Degradable sutures can be in either a braided multifilament form or a monofilament form.

“Non-degradable suture” (also referred to as “non-absorbable suture”) refers to a suture comprising material that is not degraded by chain scission such as chemical reaction processes (e.g., hydrolysis, oxidation/reduction, enzymatic mechanisms or a combination of these) or by a thermal or photolytic process. Non-degradable suture material includes polyamide (also known as nylon, such as nylon 6 and nylon 6,6), polyester (e.g., polyethylene terephthlate), polytetrafluoroethylene (e.g., expanded polytetrafluoroethylene), polyether-ester such as polybutester (block copolymer of butylene terephthalate and polytetra methylene ether glycol), polyurethane, metal alloys, metal (e.g., stainless steel wire), polypropylene, polyethelene, silk, and cotton. Sutures made of non-degradable suture material are suitable for applications in which the suture is meant to remain permanently or is meant to be physically removed from the body.

“Suture diameter” refers to the diameter of the body of the suture. It is to be understood that a variety of suture lengths may be used with the sutures described herein and that while the term “diameter” is often associated with a circular periphery, it is to be understood herein to indicate a cross-sectional dimension associated with a periphery of any shape. Suture sizing is based upon diameter. United States Pharmacopeia (“USP”) designation of suture size runs from 0 to 7 in the larger range and 1-0 to 11-0 in the smaller range; in the smaller range, the higher the value preceding the hyphenated zero, the smaller the suture diameter. The actual diameter of a suture will depend on the suture material, so that, by way of example, a suture of size 5-0 and made of collagen will have a diameter of 0.15 mm, while sutures having the same USP size designation but made of a synthetic absorbable material or a non-absorbable material will each have a diameter of 0.1 mm. The selection of suture size for a particular purpose depends upon factors such as the nature of the tissue to be sutured and the importance of cosmetic concerns; while smaller sutures may be more easily manipulated through tight surgical sites and are associated with less scarring, the tensile strength of a suture manufactured from a given material tends to decrease with decreasing size. It is to be understood that the sutures and methods of manufacturing sutures disclosed herein are suited to a variety of diameters, including without limitation 7, 6, 5, 4, 3, 2, 1, 0, 1-0, 2-0, 3-0, 4-0, 5-0, 6-0, 7-0, 8-0, 9-0, 10-0 and 11-0.

“Needle attachment” refers to the attachment of a needle to a suture requiring same for deployment into tissue, and can include methods such as crimping, swaging, using adhesives, and so forth. The suture thread is attached to the suture needle using methods such as crimping, swaging and adhesives. Attachment of sutures and surgical needles is described in U.S. Pat. Nos. 3,981,307, 5,084,063, 5,102,418, 5,123,911, 5,500,991, 5,722,991, 6,012,216, and 6,163,948, and U.S. Patent Application Publication No. US 2004/0088003). The point of attachment of the suture to the needle is known as the swage.

“Suture needle” refers to needles used to deploy sutures into tissue, which come in many different shapes, forms and compositions. There are two main types of needles, traumatic needles and atraumatic needles. Traumatic needles have channels or drilled ends (that is, holes or eyes) and are supplied separate from the suture thread and are threaded on site. Atraumatic needles are eyeless and are attached to the suture at the factory by swaging or other methods whereby the suture material is inserted into a channel at the blunt end of the needle which is then deformed to a final shape to hold the suture and needle together. As such, atraumatic needles do not require extra time on site for threading and the suture end at the needle attachment site is generally smaller than the needle body. In the traumatic needle, the thread comes out of the needle's hole on both sides and often the suture rips the tissues to a certain extent as it passes through. Most modern sutures are swaged atraumatic needles. Atraumatic needles may be permanently swaged to the suture or may be designed to come off the suture with a sharp straight tug. These “pop-offs” are commonly used for interrupted sutures, where each suture is only passed once and then tied. For barbed sutures that are uninterrupted, these atraumatic needles are preferred.

Suture needles may also be classified according to the geometry of the tip or point of the needle. For example, needles may be (i) “tapered” whereby the needle body is round and tapers smoothly to a point; (ii) “cutting” whereby the needle body is triangular and has a sharpened cutting edge on the inside; (iii) “reverse cutting” whereby the cutting edge is on the outside; (iv) “trocar point” or “taper cut” whereby the needle body is round and tapered, but ends in a small triangular cutting point; (v) “blunt” points for sewing friable tissues; (vi) “side cutting” or “spatula points” whereby the needle is flat on top and bottom with a cutting edge along the front to one side (these are typically used for eye surgery).

Suture needles may also be of several shapes including, (i) straight, (ii) half curved or ski, (iii) ¼ circle, (iv) ⅜ circle, (v) ½ circle, (vi) ⅝ circle, (v) and compound curve.

Suturing needles are described, for example, in U.S. Pat. Nos. 6,322,581 and 6,214,030; and 5,464,422; and 5,941,899; 5,425,746; 5,306,288 and 5,156,615; and 5,312,422; and 7,063,716. Other suturing needles are described, for example, in U.S. Pat. Nos. 6,129,741; 5,897,572; 5,676,675; and 5,693,072. The sutures described herein may be deployed with a variety of needle types (including without limitation curved, straight, long, short, micro, and so forth), needle cutting surfaces (including without limitation, cutting, tapered, and so forth), and needle attachment techniques (including without limitation, drilled end, crimped, and so forth). Moreover, the sutures described herein may themselves include sufficiently rigid and sharp ends so as to dispense with the requirement for deployment needles altogether.

“Needle diameter” refers to the diameter of a suture deployment needle at the widest point of that needle. While the term “diameter” is often associated with a circular periphery, it is to be understood herein to indicate a cross-sectional dimension associated with a periphery of any shape.

“Armed suture” refers to a suture having a suture needle on at least one suture deployment end. “Suture deployment end” refers to an end of the suture to be deployed into tissue; one or both ends of the suture may be suture deployment ends. The suture deployment end may be attached to a deployment device such as a suture needle, or may be sufficiently sharp and rigid to penetrate tissue on its own.

“Wound closure” refers to a surgical procedure for closing of a wound. An injury, especially one in which the skin or another external or internal surface is cut, torn, pierced, or otherwise broken is known as a wound. A wound commonly occurs when the integrity of any tissue is compromised (e.g., skin breaks or burns, muscle tears, or bone fractures). A wound may be caused by an act, such as a puncture, fall, or surgical procedure; by an infectious disease; or by an underlying medical condition. Surgical wound closure facilitates the biological event of healing by joining, or closely approximating, the edges of those wounds where the tissue has been torn, cut, or otherwise separated. Surgical wound closure directly apposes or approximates the tissue layers, which serves to minimize the volume new tissue formation required to bridge the gap between the two edges of the wound. Closure can serve both functional and aesthetic purposes. These purposes include elimination of dead space by approximating the subcutaneous tissues, minimization of scar formation by careful epidermal alignment, and avoidance of a depressed scar by precise eversion of skin edges.

‘Tissue elevation procedure” refers to a surgical procedure for repositioning tissue from a lower elevation to a higher elevation (i.e. moving the tissue in a direction opposite to the direction of gravity). The retaining ligaments of the face support facial soft tissue in the normal anatomic position. However, with age, gravitational effects and loss of tissue volume effect downward migration of tissue, and fat descends into the plane between the superficial and deep facial fascia, thus causing facial tissue to sag. Face-lift procedures are designed to lift these sagging tissues, and are one example of a more general class of medical procedure known as a tissue elevation procedure. More generally, a tissue elevation procedure reverses the appearance change that results from effects of aging and gravity over time, and other temporal effects that cause tissue to sag, such as genetic effects. It should be noted that tissue can also be repositioned without elevation; in some procedures tissues are repositioned laterally (away from the midline), medially (towards the midline) or inferiorly (lowered) in order to restore symmetry (i.e. repositioned such that the left and right sides of the body “match”).

“Medical device” or “implant” refers to any object placed in the body for the purpose of restoring physiological function, reducing/alleviating symptoms associated with disease, and/or repairing and/or replacing damaged or diseased organs and tissues. While normally composed of biologically compatible synthetic materials (e.g., medical-grade stainless steel, titanium and other metals or polymers such as polyurethane, silicon, PLA, PLGA and other materials) that are exogenous, some medical devices and implants include materials derived from animals (e.g., “xenografts” such as whole animal organs; animal tissues such as heart valves; naturally occurring or chemically-modified molecules such as collagen, hyaluronic acid, proteins, carbohydrates and others), human donors (e.g., “allografts” such as whole organs; tissues such as bone grafts, skin grafts and others), or from the patients themselves (e.g., “autografts” such as saphenous vein grafts, skin grafts, tendon/ligament/muscle transplants). Medical devices that can be used in procedures in conjunction with the present invention include, but are not restricted to, orthopedic implants (artificial joints, ligaments and tendons; screws, plates, and other implantable hardware), dental implants, intravascular implants (arterial and venous vascular bypass grafts, hemodialysis access grafts; both autologous and synthetic), skin grafts (autologous, synthetic), tubes, drains, implantable tissue bulking agents, pumps, shunts, sealants, surgical meshes (e.g., hernia repair meshes, tissue scaffolds), fistula treatments, spinal implants (e.g., artificial intervertebral discs, spinal fusion devices, etc.) and the like.

Laser-Cut Self-Retaining Sutures

As discussed above, the present invention provides laser cutting apparatus and methods for cutting retainers on suture thread. FIG. 1A illustrates a laser-cut self-retaining suture system 100. Self-retaining suture system 100 comprises needles 110, 112 attached to self-retaining suture thread 102. Self-retaining suture thread 102 includes a plurality of retainers 130 distributed on the surface of a filament 120. In lead-in section 140 of filament 120 there are no retainers 130. In section 142 of filament 120 there are a plurality of retainers 130 arranged such that the suture can be deployed in the direction of needle 110, but resists movement in the direction of needle 112. In transition section 144, there are no retainers 130. In section 146, there is a plurality of retainers 130 arranged such that the suture can be deployed in the direction of needle 112, but resists movement in the direction of needle 110. In lead-in section 148 of filament 120 there are no retainers 130. A break is shown in each of sections 140, 142, 144, 146 and 148 to indicate that the length of each section may be varied and selected depending upon the application for which the suture is intended to be used. For example, transition section 144 can be asymmetrically located closer to needle 110 or needle 112, if desired.

Self-retaining suture system 100 is composed of two arms. Each arm may be considered to be a section of self-retaining suture system 100. The first arm includes sections 142 and section 140 of self-retaining suture thread 102 and a curved needle 110 has relatively small retainer suitable for engaging harder/denser tissue. The second arm includes sections 146 and 148 and needle 112 of self-retaining suture thread 102.

Although self-retaining suture system 100 of FIG. 1A has two arms, in alternative embodiments, a self-retaining suture system has single-armed sutures; dual-armed sutures; triple-armed sutures; multiple-armed sutures; heterofunctional sutures having two or more sections of suture having different features; dual-arm sutures having different types (or sizes) of needles on each end; single or dual-armed sutures for use with different layers/depth and types of tissue; single or dual armed sutures with sections of filament having different diameters for use with different layers/depth and types of tissue.

Retainers 130 are laser-cut retainers formed on the surface of filament 120 by cutting and/or ablating portions of the filament with a laser as described below. The retainers 130 are in some embodiments identical to one another. In alternative embodiments, retainers 130, vary in shape, dimensions and/ or distribution in different sections and/or within sections of the self-retaining suture thread 102 as best suited for engaging tissue. It is an advantage of self-retaining suture system having laser-cut retainers that it is feasible to create multiple configurations of retainers on a suture thread with a single cutting device as will be described below.

FIG. 1B illustrates a magnified view of self-retaining suture thread 102 in section 142. As shown in FIG. 1B, a plurality of retainers 130 is distributed on the surface of filament 120. The affixation of self-retaining sutures after deployment in tissue entails the penetration of retainer ends 132 into the surrounding tissue resulting in tissue being caught between the retainer 130 and the body of suture filament 120. The inner surface 134 of the retainer 130 that is in contact with the tissue that is caught between the retainer 130 and the body of filament 120, is referred to herein as the “tissue engagement surface” or “inner retainer surface.” As illustrated in FIG. 1B, each retainer 130 has a tip 132 and tissue retainer surface 134. When self-retaining suture thread 102 is moved in the direction of arrow 136, retainers 130 lies flat against the body of filament 120. However, when self-retaining suture thread 102 is moved in the direction of arrow 138, tip 132 of retainer 130 engages tissue surrounding filament 120 and causes retainer 130 to fan out from filament 120 and engage the tissue with tissue engagement surface 134 thereby preventing movement of the suture in that direction.

FIG. 1C illustrates a magnified view of self-retaining suture thread 102 in section 144. As shown in FIG. 1C, in section 144, there are no retainers 130. Section 144 may be referred to as the transition section of self-retaining suture system 100. Section 144 may be deployed in either both of the directions shown by arrows 136 and 138. In many procedures it is desirable to locate the transition region in order to properly situate the transition region at the beginning of suture deployment. Thus, the filament 120 in section 144 is, in some embodiments, provided with an identifiable feature. For example, as shown in FIGS. 1A and 1C, section 144 of self-retaining suture system 100 is provided with an identifiable marker in the form of visible band 150. Band 150 represents a portion of filament 120 having a different visible characteristic than other portions of filament 120 which can thus be identified by a surgeon in order to identify and locate the transition section 144 of self-retaining suture system 100. In alternative embodiments, markers are provided on other sections of the filament and/or needles in order to identify features of the self-retaining suture system associated with the section marked. Additionally, marker differences can include different shapes, different colors, different numbers, and different letters to name a few types of markers.

FIG. 1D illustrates a magnified view of self-retaining suture thread 102 in section 146. As shown in FIG. 1D, a plurality of retainers 130 is distributed on the surface of filament 120. As illustrated in FIG. 1D, each retainer 130 has a tip 132 and tissue retainer surface 134. When self-retaining suture thread 102 is moved in the direction of arrow 138, retainer 130 lies flat against the body of filament 120. However, when self-retaining suture thread 102 is moved in the direction of arrow 136, tip 132 or retainer 130 engages tissue surrounding filament 120 and causes retainer 130 to fan out from filament 120 and engage the tissue with face 134, thereby preventing movement of the suture in that direction. Thus, in section 146 retainers 130 are oriented in the opposite direction to the retainers 130 in section 142.

FIG. 1E illustrates an alternative embodiment of a self-retaining suture system 160. Self-retaining suture system 160 includes needle 110 and sections 140, 142 and 144 of self-retaining suture system 100 of FIG. 1A. However, self-retaining suture system 160 is a single-armed system. As shown in FIG. 1E, filament 120 terminates following section 146 in a tissue anchor 114 e. Tissue anchor 114 e is a device for engaging tissue and preventing filament 120 from moving through tissue in the direction of needle 110. Tissue anchor 114 e is in some embodiments formed in one piece with filament 120 or formed separately and subsequently attached to filament 120. As shown in FIG. 1E, tissue anchor 114 e has a bar-shaped body 170 e which extends approximately perpendicular to the axis of filament 120. Bar-shaped body 170 e is sufficiently long and stiff to preclude movement of filament 120 in the direction of needle 110 after tissue anchor 114 e has engaged a tissue.

FIG. 1F shows an alternative anchor 114 f which could be used in place of tissue anchor 114 e of FIG. 1E. As shown in FIG. 1F, tissue anchor 114 f comprises a conical body 170 f. Conical body 170 f has a pointed end 172 f and tissue engaging features 174 f which consist of ribs and/or barbs. Tissue anchor 114 f is configured to be pushed into tissue in order to anchor filament 120 to that tissue and preclude movement of filament 120 in the direction of needle 110.

FIG. 1G shows an alternative anchor 114 g which could be used in place of tissue anchor 114 e of FIG. 1E. As shown in FIG. 1G, tissue anchor 114 g comprises a loop 170 g. Loop 170 g is, in this embodiment, formed by folding back the end 172 g of filament 120 and securing end 172 g to filament 120 by welding, fusing and/or adhesive. Loop 170 g is thus formed from the material of filament 120. Loop 170 g has an aperture 174 g through which needle 110 can pass in order to create a noose which can be used to engage tissue and preclude movement of filament 120 in the direction of needle 110.

FIG. 1H shows an alternative anchor 114 h which could be used in place of tissue anchor 114 e of FIG. 1E. As shown in FIG. 1H, tissue anchor 114 h comprises a staple-shaped body 170 h. Filament 120 passes through an aperture in anchor 114 h and is secured by a crimp 174 h. Staple-shaped body 170 h has two points pointed end 172 h which can be deformed towards each other to engage tissue and preclude movement of filament 120 in the direction of needle 110.

Laser-Machining System for Creating Self-Retaining Sutures

In embodiments of the present invention, a laser machining system is provided and utilized to create retainers on the surface of a suture thread and/or provide visible markings on the suture thread. The laser machining system uses a focused beam of coherent light to selectively cut and/or ablate material from a suture thread to generate retainers having a desired configuration on the suture thread. The cutting/ablating process is a noncontact process. A suitable laser machining system has very high spatial confinement and control and very low heat deposition to the suture thread so as to prevent damage to the suture thread during retainer formation.

In general, a laser machining system is used to apply a laser beam to a volume of material within a suture thread. The laser energy is absorbed by the material which is thereby vaporized and removed. The suture thread is, in some embodiments, provided with a component which promotes absorption of the laser energy. The laser light is provided at power, wavelength, and pulse duration selected to vaporize the selected volume of suture material without damaging the remaining suture thread. The wavelength of the laser is typically in the range of UV to visible to infrared light. Light as used herein is not limited to the visible spectrum. The ideal wavelength or spectrum of wavelengths is selected to achieve the best cutting/ablation characteristics.

The exposure required to cause the ablation/cutting may be accomplished in one continuous exposure or a plurality of pulses. Exposure to a plurality of laser pulses allows the energy of each laser pulse to dissipate and therefore induces a lower temperature rise in the suture thread than one continuous pulse of the same total length. The power of the laser beam and/or pulse duration are controlled to cut/ablate the desired material while delivering insufficient total energy to the surrounding material to adversely affect the bulk material properties of the suture thread. For example, in a preferred embodiment a femtosecond laser is used which provides high power for very short duration laser pulses. The wavelength, power, focus and/or pulse duration are also controlled to achieve the desired penetration of the laser into the suture thread.

A variety of different lasers and control system can be used to direct the laser to the selected locations of a suture to create the retainers. In some embodiments, a steered beam system is used to achieve the desired cutting/ablation. In a steered beam system a pulsed laser is directed at a moving point on the suture thread. Mirrors mounted on computer-controlled galvanometers are used to direct the laser beam at targeted volumes of the suture thread. In alternative embodiments, a mask or other optics are used to generate a shaped laser beam having a suitable shape for achieving the desired cutting/ablation. In alternative embodiments, a stepwise pattern is used to create the laser marked indicia. A volume of the suture material is targeted and ablated/cut by modulating a laser on and off The suture and/or laser is then moved to align a new target volume with the laser and the new target is ablated/cut by modulating the laser on and off. The process is continued to direct the beam stepwise or to move the suture thread stepwise until the desired retainer configuration is achieved.

FIG. 2A is a schematic diagram of a laser-machining system suitable for manufacturing self-retaining sutures. As shown in FIG. 2A, a laser-machining system 200 includes five subsystems. The five subsystems of laser-machining system 200 are laser subsystem 210, optics subsystem 220, imaging subsystem 230, transport subsystem 240 and control subsystem 250. Laser subsystem 210 supplies laser power to laser machining system 200 in the form of laser beam 202. Laser subsystem 210 is under control of control subsystem 250. Laser subsystem 210 includes laser 212, laser attenuator 214 and laser homogenizer 216. Laser 212 generates laser beam 202. Laser attenuator 214 modulates laser beam 202, allowing it to pass and blocking it as necessary under control of control subsystem 250. Laser homogenizer 216 modifies the laser beam 202 to produce an even power density across laser beam 202.

In a preferred embodiment, laser subsystem 210 is a femtosecond laser system. A femtosecond laser system provides ultra short pulses of laser energy suitable for cutting/ablating material from a suture thread with a high degree of accuracy and without causing damage to the surrounding suture thread. By using femtosecond laser pulses, the laser energy is deposited into small volumes of material by optical absorption followed by avalanche ionization of the material. The laser energy is deposited at a time scale much shorter than the timescale for heat transport in the material. Thus, the material targeted by the laser beam is transformed from solid to vapor phase and to plasma formation almost instantaneously and without significant heat transfer to the surrounding material. The femtosecond laser pulses thus reduce thermal damage to the suture thread.

A femtosecond laser is advantageous because it can achieve: high resolution and repeatability in a fully automated system; high aspect ratios for cutting/ablation of suture thread with low redeposition of ablated material; very localized effects and little damage to suture thread adjacent cutting/ablation zone; and effective cutting of suture thread material over a wide range of materials and diameters (including, for example USP 12-0 to 7). For example, a femtosecond laser system can cut/ablate suture material with submicron resolution and nanometer scale surface roughness of cut surfaces. The parameters of the femtosecond laser can be adjusted to achieve the desired resolution, aspect ratio and reduce collateral damage including by selecting: the appropriate wavelength or combination of wavelengths; the power distribution of the beam (Gaussian, Top hat, axiconic to provide an annular ring profile); the beam energy and pulse duration; and the focal length and depth of focus for the optics system. The parameters are in some cases modified for different suture thread materials and diameters and retainer configurations.

Laser beam 202 passes from laser subsystem 210 to optics subsystem 220. Optics subsystem 220 includes one or more mirrors 222 and lenses for directing and/or focusing laser beam 202 at a desired target. In particular, optics subsystem 220 includes an object lens 224 from which laser beam 202 leaves optic subsystem 220 towards the desired target. Optics subsystem 220 also includes one or more actuators 226, 228 under control of computer subsystem 250 for adjusting the positions of the mirror(s) 222 and lens(es) 224.

Imaging subsystem 230 allows observation of suture thread 204 and monitoring of the results of laser machining upon it. Imaging subsystem 230 includes an imaging device 232 which is in some embodiments a camera. Imaging system also includes an illumination device 234 for illuminating suture thread 120. Imaging subsystem 230 can also include one or more mirrors and lenses for directing light to and from suture thread 202. Imaging subsystem 230 provides images of suture thread 204 to control subsystem 250. In a preferred embodiment, imaging subsystem 230 is provided in-line with optics subsystem 220 as shown. That is to say that illumination device 234 delivers illumination to suture thread 204 and imaging device 232 receives an image of suture thread 204 through the optic subsystem 220. The images of suture thread 204 can be used by control subsystem 250 to verify the correct operation of the laser subsystem 210 and optics subsystem 220 and make configuration adjustments as necessary. Advantageously image data from the imaging subsystem 230 can be used by the control subsystem 250 to monitor and adjust the depth of focus of the optic system to allow proper focusing and targeting of the laser beam. In alternative embodiments, an off-line imaging system can be used. The images of the suture thread 204 can also be used for quality control of retainer formation including, in some embodiments, validating the correct creation of 100% of the retainers.

Transport subsystem 240 operates to support suture thread 204 and move suture thread 204 relative to laser beam 202. The laser subsystem 210, imaging subsystem 230, optics subsystem 220 and transport subsystem 240 are all securely mounted to a bench 206 to prevent relative movement/vibration of the systems except as controlled by transport subsystem 240. Transport subsystem 240 includes chucks 242 for holding each end of suture thread 204. Chucks 242 are preferably driven by an actuator 243 which drives rotation of suture thread 204 around the longitudinal axis of the suture thread 204. Chucks 242 are mounted to an XY positioning stages 244, 246. XY positioning stages 244, 246 are preferably driven by actuators 245, 247 which control the position of the suture thread 204 relative to the laser beam 202. XY positioning stages 244, 246 are preferably aligned with the longitudinal axis of suture thread 204 such that one stage controls movement of the suture thread along its longitudinal axis relative to laser beam 202 and the other stage controls movement of suture thread 204 perpendicular to the longitudinal axis (across the laser beam 204). Actuators 243, 245, 247 are preferably under the control of control subsystem 250. Transport subsystem 240, in some embodiments, includes a suture spool and mechanism (not shown) for automatically feeding lengths of suture thread to be held between chucks 242 without the need for rethreading the suture thread.

Transport subsystem 240 also includes a stabilization device 248 for stabilizing suture thread 204 adjacent the laser beam 202. Stabilization device 248 reduces movement of suture thread 204 adjacent the cutting region in order to enhance the accuracy of the laser machining operation. In preferred embodiment stabilization device 248 is an air bearing which provides a stream of air to stabilize suture thread 204 without mechanically contacting suture thread 204. The stream of air also serves to cool the suture thread 204 and eliminate smoke and particles from the cutting region.

Control subsystem 250 is a general purpose machine control system having outputs for controlling actuators and inputs for receiving data from machine sensors. Control subsystem 250 includes memory for program and data storage. The program and data storage includes parameters for operation of the laser subsystem 210, optics subsystem 220, imaging subsystem 230, and transport subsystem 240 and/or recorded diagnostic and performance data concerning the operation of laser machining system 200. Data may be stored in control subsystem 250 or other data storage associated with the local network or WAN. Data may be stored in a single format or in multiple formats. Data may be stored on a single type of media or on multiple types of media e.g. hard disks, RAM, flash memory, floppy disks, web-storage systems, etc.

Control subsystem 250 includes one or more processors 252 which can be a computer processer, CPU, and typically includes a microcontroller, CPU, microprocessor or equivalent control circuitry or processor, designed specifically for controlling the laser machining system 200, and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. The control system contains and/or has access to programs and/or data which define the distribution of retainers to be formed on a filament and the shape/shapes of the retainers to be formed on the filament as well as the tolerances for the expected shape/shapes of the retainers. The details of the design of control subsystem 250 are not critical to the present invention. Rather, any suitable control subsystem 250 may be used that carries out the functions described herein. The use of computer/microprocessor-based control systems for controlling machine tools is well known in the art.

In an embodiment, the laser beam provided by laser subsystem 210 and optic subsystem 220 has a Gaussian power density distribution. FIG. 2B shows a representative image of a Gaussian laser beam 260 incident on a planar surface 268. As shown in FIG. 2B, the power density of Gaussian beam 260 drops off rapidly moving away from a peak at the center 262 of the beam 260. The diameter D of the zone of peak power density can be altered using the optic subsystem to focus the laser beam. FIG. 2C shows a graphical representation of the power density distribution of Gaussian laser beam (such as laser beam 260 of FIG. 2B).

An alternative laser beam shape/power distribution can be achieved by the use of an axicon prism system utilizing two axicon (rotationally revolved prism) and a lens. The first axicon produces a ring, the lens focuses the ring to a thin (5 micron) width and the second axicon collimates the ring. Varying the distance between the axicon prisms provides the ability to control the diameter of the ring from 0 microns to 300 microns while maintaining focus. The axicon prism system can be used to machine cones into the suture material at an angle. Cones of various diameters are used in a laser machining process to remove material from a filament. By adjusting the cone diameter and the angle of cone relative to the retainer/filament a wide variety of retainer configuration can be machined which would not be possible with a standard laser beam or mechanical cutting. For example, the cone produced by the axicon pair is in some embodiments set to be near 0 diameter, progressively getting larger while the focus of the laser is translated into the suture removing a 3D cone shape of suture material (at a compound angle relative to a retainer to be formed). The laser power is coordinated with the cone diameter to maintain a constant energy density in the ring regardless of ring diameter.

FIG. 2D shows a representative image of a laser beam 270 from an axicon prism system incident on a planar surface 278. As shown in FIG. 2E the laser beam has a low power density at the center 272. The power density increases travelling away from center 272 until it peaks in ring 274. The power density then drops off rapidly moving outward from ring 274. The diameter D of ring 274 can be controlled by changing the distance between the axicon prisms. The thickness T of the ring can be controlled using the lens between the axicon prisms to focus the ring. FIG. 2E shows a graphical representation of the power density distribution of a laser beam (such as laser beam 270 of FIG. 2D) from an axicon prism system, where the axicon prism essentially creates an energy distribution having a profile in the form of an annular ring.

FIG. 3A shows a sectional view of an embodiment of a stabilization device 248 for stabilizing suture thread 204 adjacent the laser beam 202 (see FIG. 2A). The stabilization device 248 reduces movement of suture thread 204 adjacent the cutting region in order to enhance the accuracy of the laser machining operation (see FIG. 2A). As shown in FIG. 3A, a preferred embodiment of stabilization device 248 is an air bearing 300 which provides a stream of air to stabilize suture thread 304 without mechanically contacting suture thread 304. FIG. 3A shows a sectional view of an air bearing 300 which can be included in stabilization device 248 of FIG. 2A. As shown in FIG. 3A, air bearing comprises an entry nozzle 310 and an exit nozzle 320. Entry nozzle 310 and exit nozzle 320 have tips 312, 322 which have an inside diameter as close as possible to the diameter of the suture without running the risk of making physical contact. The inside diameter may be 1.5, 2.0, 2.5 or 3.0 times the suture diameter, however as the inside diameter increases, there is a greater tendency for looseness in the fluid film bearing. Thus, it is preferred to have the inside diameter under two times the suture diameter, and more preferably less than 1.5 times the suture diameter. In preferred embodiments, different nozzles are used for suture threads of different size. Entry nozzle 310 and exit nozzle 320 can be made by drawing down a glass tube to the appropriate diameter for a particular suture thread and cutting and grinding the tip 312, 322. An alternative and suitable air bearing is available from Newway Air Bearings (Aston, Pa.) which incorporates graphite porous media for the bearing and utilizes the air brushing approach in a size suitable for sutures.

As shown in FIG. 3A, exit nozzle 320 is mounted within a cavity 332 of a manifold 330. O-rings 340, 342 seal exit nozzle 320 to the surface of cavity 332. Manifold 330 is machined to deliver pressurized air from an intake line 334 evenly around cavity 332. Entry nozzle 310 is positioned with tip 312 within the lumen of exit nozzle 320 as shown. Entry nozzle 310 and exit nozzle 320 are positioned coaxially. Entry nozzle 310 is aligned and secured in position by entry cap 350. An o-ring 344 seals entry nozzle 310 to entry cap 350. Entry cap 350 has a chamfered entry port 352 which is positioned coaxial with entry nozzle 310 and exit nozzle 320. An exit cap 354 is mounted on the other end of manifold 330. Exit cap 354 has an exit port 356 through which exit nozzle 320 protrudes. Entry cap 350, manifold 330 and exit cap 354 are secured together by a plurality of fasteners 358.

A suture thread 304 can be introduced through entry port 352. Suture thread 304 passes through entry nozzle 310 and then through exit nozzle 320 passing out of tip 322 of exit nozzle 320 as shown. Pressurized air is introduced through intake 334 and passes into the cavity 332 of manifold 330. The pressurized air the passes into exit nozzle 320 and is forced out of tip 322 surrounding suture thread 304. (Some air also leaks out through entry nozzle 310). The fast moving air surrounding suture thread 304 operates as an air bearing stabilizing the position of suture thread 304 adjacent tip 322 without contacting suture thread 304.

FIG. 3B, shows a perspective view only of exit nozzle 320 and suture thread 304. As shown in FIG. 3B pressurized air enters the lumen 324 of exit nozzle 320 (arrows 360 and is forced at high speed out of the narrow tip 322 of exit nozzle (arrows 362). The stream of air within tip 322 stabilizes suture thread within the center of tip 322 and so suture thread does not contact the walls of exit nozzle 320. Furthermore, a stream of high speed air surrounds suture thread 304 as it exits tip 322. The tip is designed to produce laminar flow of air in this stream in an area adjacent the tip. In this laminar flow zone, the high speed stream of air stabilizes the suture thread damping movement and vibration caused e.g. by the cutting process. Pressure is exerted by slower moving gas on the outside of the high speed stream forcing suture thread 304 to the center of stream as shown by arrows 364. Thus, the suture thread 304 is stabilized by the air bearing in the region 370 adjacent tip 322 of exit nozzle 320. The air bearing 300 is positioned so that stabilization region 370 is positioned in the cutting zone of the laser. The stream of air passing over suture thread 304 also serves to remove particulates and smoke from the laser cutting process and also cools the suture thread 304 during cutting by the laser. The suture thread is passes out of the tip 332 of exit nozzle 320 for cutting of retainers in the stabilization zone. After cutting the retainers are moved away from exit nozzle 320. It is preferred that the retainers not move into the exit nozzle as the high velocity air can damage the retainers, and the retainers can cause turbulence in the high velocity air destabilizing the suture thread in stabilization region 370.

For cutting USP 2-0 blue polypropylene suture material without an air bearing (See FIGS. 3A-3B) the following femtosecond laser parameters were found effective: a 10× objective 0.26 N.A. lens; 26 mW average laser power; 775 nm laser wavelength: (frequency doubled and mode locked erbium fiber laser with Titanium Sapphire chirped pulse amplifier; a pulse width 122 femtoseconds; an RF Divider establishing a 3 kHz pulse rate; and a cutting speed of 9.5 mm/minute. The best cutting results were achieved by penetrating the suture within the body of the filament and then moving outward to edge. For cutting USP 4-0 blue propylene suture material the following femtosecond laser parameters were found effective: a 20× objective lens, 36 mW average laser power; and a cutting speed of 10 mm/minute. With these parameters each retainer took only 1.16 second to create. Addition of an air bearing allowed retainers to be created more effectively on USP 2-0, 4-0 and 6-0 blue polypropylene suture material because of e.g. stabilization of the filament and cooling of the filament during cutting. However, use of UV wavelengths was found to be more effective for cutting the blue polypropylene suture material as it vaporizes the suture material more effectively with less heating of surrounding material. In a preferred embodiment a combination of UV and IR wavelength is used to ablate material with about 70% or more of the energy being supplied in the UV wavelength.

FIG. 4A is a flowchart of a method 400 for operating the laser machining system 200 of FIG. 2A. In the first step 402, the suture thread is mounted to the chucks of the transport system. The suture thread should also be tensioned to a desired tension during the mounting step. The tension should be the same for each suture thread. At step 404, the control system operate the transport subsystem is operated to index and rotate the suture thread to the correct position for forming the first retainer. The distribution/location of retainers is stored in a retainer distribution pattern data or program file. At step 406, the control subsystem selects the correct retainer creation pattern for the indexed location on the suture thread. The retainer creation pattern dictates the final orientation, shape and size of the retainer to be created at a particular location.

The laser machining system is then operated to form a retainer at the indexed location in accordance with the selected retainer creation pattern. At step 408, the transport system is operated to align a target volume of the suture thread with the laser. At step 410, the laser subsystem is operated to ablate/cut material in the target volume. Step 410 can also include validation of the ablation/cutting using the imaging subsystem. At step 412, if further material needs to be ablated/cut to form the retainer, the process returns to step 408 to operate the transport system to align a new target volume with the laser in accordance with the retainer creation pattern. At step 412, if the laser creation pattern is completed, the process moves on to step 414.

At step 414, the imaging subsystem is operated to image the completed retainer and provide the image data to the control subsystem. The control subsystem uses the image data to validate that the retainer is within the tolerances defined by the retainer creation pattern. If the retainer cannot be validated, the control system can do one or more of: operate the transport subsystem and laser subsystem to correct the defect; fail the particular suture thread; mark an exception with respect to the suture thread for further inspection; set an alert for a human operator; and/or shut down operation of the laser-machining system. If the retainer is validated within tolerances at step 414 the process moves on to step 416. At step 416, if further retainers remain to be created, the process return to step 404 for indexing the suture thread to the next position for creating a retainer. At step 416, if all retainers have been completed, the process moves to step 418. At step 418 the suture thread is complete and is unloaded from the chucks.

FIGS. 4B-4D further illustrate steps in the process of forming a retainer according to the method of FIG. 4A. As shown in FIG. 4B, the suture thread 424 is moved longitudinally 430, laterally (432) and axially (434) by the transport subsystem to align the laser beam 426 with a target volume of the suture thread 424. The laser subsystem is then operated to ablate material from the suture thread 424, generating a cavity or slot 428. Note that cavity 428 is larger in diameter than laser beam 426. In an embodiment, a laser beam 3 nm in diameter generates a cavity of approximately 7 nm in diameter.

As shown in FIG. 4C, the suture thread 424 is moved longitudinally 430 and laterally 432 stepwise to a series of positions aligning new target volumes with the laser beam to generate a series of cavities through suture thread 424. The target volumes are dictated by the suture creation pattern. Note that it is preferable to make interior cuts to form the tissue engagement surface of the retainer prior to cutting the tip of the retainer.

FIG. 4D shows the completed retainer 440 having a tip 442 and retainer engagement surface 444. Note that tip 442 is not elevated above the surface of suture thread 424. Post-cut processing can be carried out in some cases to elevate the tip above the surface of the suture thread 424. In other embodiments, the retainer 440 is designed to be effective without elevation of the retainer tip 442 above the original surface of the suture thread 424. The same steps are repeated for the remaining retainers on suture thread 424. Note that different configurations and orientations of retainer can be created at different locations on the suture using a different retainer creation pattern without requiring a different cutting head or reloading the suture thread. An advantage of utilizing a laser-machining system to create retainers is the ability to form retainers in configurations that are difficult and/or impossible to make using mechanical cutting with a blade.

A retainer was cut on USP 2-0 blue polypropylene suture thread. The retainer was removed and the laser-cut surface of a self-retaining suture was examined for flatness and uniformity. The laser-cut tissue engagement surface of the retainer (not shown) should have similar characteristics of flatness and uniformity. FIG. 5 shows an image of the examined laser cut surface 922 machined into a suture thread 920. FIG. 6 shows a graph of the profile of laser-cut surface viewed laterally. The laser machining system is shown to make laser-cut surfaces of high flatness and uniformity with high precision and repeatability to create a self-retaining suture.

FIG. 7 show a range of retainer distributions and patterns that can be created using the laser machining system. FIG. 7 shows a single helix distribution which may be cut with the laser machining system of the present invention. The laser-cut retainers can have any laser-cut retainer configuration described herein and/or different laser-cut retainer configurations can be present at different points of the self-retaining suture. Note also that the laser machining system of the present invention is capable of creating non-uniform retainer distributions along a single suture thread if advantageous for a particular self-retaining suture application.

Referring first to FIG. 7 which shows a single helix distribution of laser-cut retainers 704 on a self-retaining suture 700. As shown in FIG. 7, the self-retaining suture 700 has a filament 702 which is of USP 2-0, 4-0, 6-0, 7-0, 8-0, 9-0, 10-0, 11-0, 12-0 or below. As shown in FIG. 7, the filament is 0.25 mm in diameter which is a 4-0 suture. The self-retaining suture 700 includes a plurality of laser-cut retainers 704 arranged in a helical pattern around and along the filament 702. As shown in FIG. 7, the helix has a pitch of 4.46 mm (or 5.7 twists per inch). The distance between the base of one laser-cut retainer and the base of the adjacent laser-cut retainer in the same helix is 0.6 mm—measured axially—see arrow 718. In an embodiment, the self-retaining suture has a barbed section 712 at least 70 mm in length and a 100 mm unbarbed lead 710, 714 on either side of the barbed section 712. The barbed section 712 may have retainers 704 in one orientation or in different orientations. Note that because the laser machining system is contactless, retainer distribution patterns can be designed without limitations imposed by the need to support a suture without impairing already cut retainers during mechanical cutting. Thus, for example, in some embodiments, the pitch can be less than the length of a retainer.

Note that because the laser machining system is contactless, retainer distribution patterns can be designed without limitations imposed by the need to support a suture without impairing already cut retainers during mechanical cutting. Thus, for example, in some embodiments the pitch can be less than the length of a retainer.

Examples of Self-Retaining Sutures with Laser-Cut Retainers

FIGS. 8A-8B are images of examples of laser-cut retainers created with the laser cutting system of FIG. 2A. Self-retaining sutures comprising suture threads with a plurality of laser-cut retainers thereon made to test the capabilities of a laser-machining system in accordance with FIG. 2A. The suture threads were, in each case blue-colored propylene filaments.

FIG. 8A shows an image of 2-0 polypropylene suture 820 having laser-cut retainers 822 thereon. Laser-cut retainers 822 have a straight cut configuration and are distributed in a double-helix distribution. After the retainers 822 were cut, the suture 820 was heat treated for five minutes at 155 C while under 32 grams of tension to elevate the retainers 822.

FIG. 8B shows an image of 10-0 polypropylene suture 800 having laser-cut retainers 802 thereon. Laser-cut retainers 802 have a straight cut configuration.

FIG. 8C shows an image of a polypropylene suture 860 having laser-cut retainers 862 thereon. Laser-cut retainers 862 have a straight cut configuration and are distributed in a double-helix distribution. After the retainers 862 were cut, the suture 860 was heat treated for five minutes at 155 C to elevate the retainers 862. The resulting parameters L1-L5 of suture 860 were then measured under a microscope. The suture diameter L1 was 101.8 nm; the cut length L2 was 99.5 nm; the cut depth L3 was 34.5 nm; the elevation L4 of the tip of the retainer above the surface of the filament was 15.8 nm; and the distance L5 between adjacent retainers was 118.3 nm.

FIG. 8D shows an image of a polypropylene suture 870 having laser-cut retainers 872 thereon. Laser-cut retainers 872 have a straight cut configuration and are distributed in a double-helix distribution. After the retainers 872 were cut, the suture 870 was heat treated for five minutes at 155 C to elevate the retainers 872. The resulting parameters L1-L4 and AN1 of suture 870 were then measured under a microscope. The suture diameter L3 was 103.8 nm; the cut depth L2 was 29.7 nm; the elevation L1 of the tip of the retainer above the surface of the filament was 14.6 nm; the distance L4 between adjacent retainers was 131.3 nm; and the angle AN1 was 14.3 degrees.

FIG. 8E shows an image of a polypropylene suture 880 having laser-cut retainers 882 thereon. Laser-cut retainers 882 have a straight cut configuration and are distributed in a double-helix distribution. After the retainers 882 were cut, the suture 880 was heat treated for five minutes at 155 C to elevate the retainers 882. The resulting parameters L1-L6 of suture 880 were then measured under a microscope. The suture diameter L6 was 93.3 nm; the width L1 of the retainer base was 77.6 nm; the cut length L3 was 69.2 nm; the cut depth L4 was 28.5 nm; the elevation L5 of the tip of the retainer above the surface of the filament was 14.6 nm; and the distance L2 between adjacent retainers was 89.1 nm.

FIG. 8F shows an image of a polypropylene suture 890 having laser-cut retainers 892 thereon. Laser-cut retainers 892 have a straight cut configuration and are distributed in a double-helix distribution. After the retainers 892 were cut, the suture 890 was heat treated for five minutes at 155 C to elevate the retainers 892. The resulting parameters L1-L6 and AN1 of suture 890 were then measured under a microscope. The suture diameter L5 was 96.5 nm; the width L6 of the retainer base was 83.4 nm; the cut length L1 was 107.9 nm; the cut depth L2 was 37.0 nm; the elevation L3 of the tip of the retainer above the surface of the filament was 21.2 nm; the distance L4 between adjacent retainers was 117.2 nm; and angle An1 was 18 degrees.

Materials

Suture threads described herein may be produced by any suitable method, including without limitation, injection molding, stamping, cutting, laser, extrusion, and so forth. The suture threads described herein may use any material conventionally used for the manufacture of sutures including for example, metals and metal alloys, polymers including non-degradable polymers and biodegradable polymers, and natural materials. With respect to cutting, polymeric suture threads/filaments may be manufactured or purchased for the suture body, and the retainers can be subsequently cut onto the suture body. During cutting, either the laser beam or the suture thread may be moved relative to the other, or both may be moved, to control the size, shape and depth of the retainers.

It is an advantage of the laser-machining system described herein that it is operative to form retainers on a wide range of suture materials. Suitable suture materials include: degradable suture materials, non-degradable suture materials, natural suture materials, recombinant suture materials and metallic suture materials. Degradable suture materials (also referred to as “biodegradable suture” or “absorbable suture”) are those which, after introduction into a tissue are broken down and absorbed by the body. Typically, the degradation process is at least partially mediated by, or performed in, a biological system. “Degradation” refers to a chain scission process by which a polymer chain is cleaved into oligomers and monomers. Chain scission may occur through various mechanisms, including, for example, by chemical reaction (e.g., hydrolysis, oxidation/reduction, enzymatic mechanisms or a combination of these) or by a thermal or photolytic process. Polymer degradation is, in some embodiments, characterized, for example, using gel permeation chromatography (GPC), which monitors the polymer molecular mass changes during erosion and breakdown. Non-degradable suture materials (also referred to as “non-absorbable suture”) are those which are not degraded by chain scission such as chemical reaction processes (e.g., hydrolysis, oxidation/reduction, enzymatic mechanisms or a combination of these) or by a thermal or photolytic process.

Degradable suture materials include polymers for example polyglycolic acid, copolymers of glycolide and lactide, copolymers of trimethylene carbonate and glycolide with diethylene glycol (e.g., MAXON™, Tyco Healthcare Group), terpolymer composed of glycolide, trimethylene carbonate, and dioxanone (e.g., BIOSYN™ [glycolide (60%), trimethylene carbonate (26%), and dioxanone (14%)], Tyco Healthcare Group), copolymers of glycolide, caprolactone, trimethylene carbonate, and lactide (e.g., CAPROSYN™, Tyco Healthcare Group). A dissolvable suture can also include partially deacetylated polyvinyl alcohol. Polymers suitable for use in degradable sutures can be linear polymers, branched polymers or multi-axial polymers. Examples of multi-axial polymers used in sutures are described in U.S. Patent Application Publication Nos. 2002/0161168, 2004/0024169, and 2004/0116620. Sutures made from degradable suture material lose tensile strength as the material degrades. Degradable sutures can be in either a braided multifilament form or a monofilament form.

Non-degradable suture materials include, for example, polyamide (also known as nylon, such as nylon 6 and nylon 6,6), polyester (e.g., polyethylene terephthlate), polytetrafluoroethylene (e.g., expanded polytetrafluoroethylene), polyether-ester such as polybutester (block copolymer of butylene terephthalate and polytetra methylene ether glycol), polyurethane, metal alloys, metal (e.g., stainless steel wire), polypropylene, polyethelene, silk, and cotton. Sutures made of non-degradable suture material are suitable for applications in which the suture is meant to remain permanently in the body or is meant to be physically removed from the body after it has served its intended purpose.

Clinical Uses

In addition to the general wound closure and soft tissue repair applications, self-retaining sutures can be used in a variety of other indications.

Self-retaining sutures described herein may be used in various dental procedures, i.e., oral and maxillofacial surgical procedures and thus may be referred to as “self-retaining dental sutures.” The above-mentioned procedures include, but are not limited to, oral surgery (e.g., removal of impacted or broken teeth), surgery to provide bone augmentation, surgery to repair dentofacial deformities, repair following trauma (e.g., facial bone fractures and injuries), surgical treatment of odontogenic and non-odontogenic tumors, reconstructive surgeries, repair of cleft lip or cleft palate, congenital craniofacial deformities, and esthetic facial surgery. Self-retaining dental sutures may be degradable or non-degradable, and may typically range in size from USP 2-0 to USP 6-0.

Self-retaining sutures described herein may also be used in tissue repositioning surgical procedures and thus may be referred to as “self-retaining tissue repositioning sutures”. Such surgical procedures include, without limitation, face lifts, neck lifts, brow lifts, thigh lifts, and breast lifts. Self-retaining sutures used in tissue repositioning procedures may vary depending on the tissue being repositioned; for example, sutures with larger and further spaced-apart retainers may be suitably employed with relatively soft tissues such as fatty tissues.

Self-retaining sutures described herein may also be used in microsurgical procedures that are performed under a surgical microscope (and thus may be referred to as “self-retaining microsutures”). Such surgical procedures include, but are not limited to, reattachment and repair of peripheral nerves, spinal microsurgery, microsurgery of the hand, various plastic microsurgical procedures (e.g., facial reconstruction), microsurgery of the male or female reproductive systems, and various types of reconstructive microsurgery. Microsurgical reconstruction is used for complex reconstructive surgery problems when other options such as primary closure, healing by secondary intention, skin grafting, local flap transfer, and distant flap transfer are not adequate. Self-retaining microsutures have a very small caliber, often as small as USP 9-0, USP 10-0, USP 11-0 or USP 12-0, and may have an attached needle of corresponding size. The microsutures may be degradable or non-degradable.

Self-retaining sutures as described herein may be used in similarly small caliber ranges for ophthalmic surgical procedures and thus may be referred to as “ophthalmic self-retaining sutures”. Such procedures include but are not limited to keratoplasty, cataract, and vitreous retinal microsurgical procedures. Ophthalmic self-retaining sutures may be degradable or non-degradable, and have an attached needle of correspondingly-small caliber. In addition, the self-retaining sutures disclosed herein can be used in a variety of veterinary applications for a wide number of surgical and traumatic purposes in animal health.

Thus, as described more fully herein, the present invention includes, in some embodiments, laser cutting systems, components and methods as identified in the following numbered paragraphs:

A method for making a self-retaining suture comprising;

-   (a) identifying a tissue retainer location on the suture thread; -   (b) directing a laser beam at the tissue retainer location on the     suture thread; -   (c) using the laser beam to remove a volume of material defining a     slot from said suture thread, wherein the slot defines a tissue     engagement surface of a tissue retainer; -   (d) repeating steps (a), (b) and (c) to generate a plurality of     tissue retainers on the suture thread.

The method of paragraph 115, wherein step (c) comprises

-   (c1) using the laser beam to remove a volume of material defining a     slot from said suture thread, wherein the slot defines a tissue     engagement surface of a tissue retainer; and -   (c2) using the laser beam to remove a wedge-shaped volume of     material from said suture thread adjacent the slot to provide an     entrance ramp which promotes engagement of tissue by said tissue     engagement surface.

The method of paragraph 115, wherein step (b) comprises directing a laser beam at the tissue retainer location on the suture thread and focusing the laser beam to a diameter no greater than 5 μm.

The method of paragraph 115, wherein step (b) comprises directing a femtosecond laser beam at the tissue retainer location on the suture thread.

The method of paragraph 115, wherein step (b) comprises directing a femtosecond laser beam comprising infrared wavelengths at the tissue retainer location on the suture thread.

The method of paragraph 115, wherein step (b) comprises directing a femtosecond laser beam comprising ultraviolet wavelengths at the tissue retainer location on the suture thread.

The method of paragraph 115, further comprising:

-   (e) after completion of step (d), treating the suture thread to     cause a tip of each of said plurality of retainers to elevate above     a surface of said suture thread.

The method of paragraph 115, further comprising:

-   (e) after completion of step (d) heating the suture thread to cause     a tip of each of said plurality of retainers to elevate above a     surface of said suture thread.

The method of paragraph 115, further comprising:

-   (e) after completion of step (d) applying tension to the suture     thread to cause a tip of each of said plurality of retainers to     elevate above a surface of said suture thread.

The method of paragraph 115, further comprising:

-   (e) after completion of step (d) applying heat and tension to the     suture thread to cause a tip of each of said plurality of retainers     to elevate above a surface of said suture thread.

The method of paragraph 115, further comprising:

-   (e) after completion of step (d) treating the suture thread to cause     a tip of each of said plurality of retainers to elevate above a     surface of said suture thread; and -   (f) annealing the suture thread to cause a tip of each of said     plurality of retainers to remain elevated above the surface of said     suture thread.

A laser-machining system adapted to make tissue retainers on a suture thread, wherein the laser-machining system comprises:

a laser subsystem adapted to provide a laser beam;

an optic system adapted to receive the laser beam and generate a focused laser beam directed at a volume of the suture thread;

a transport subsystem adapted to move the suture thread relative to the laser beam;

an imaging subsystem adapted to image the suture thread and generate image data; and

a control subsystem adapted to receive said image data from the laser subsystem and transport subsystem to create a tissue retainer of a selected configuration at a selected location on said suture thread.

The laser-machining system of paragraph 126, wherein:

the laser subsystem comprises a femtosecond laser.

The laser-machining system of paragraph 126, wherein:

the laser subsystem comprises a UV laser.

The laser-machining system of paragraph 126, wherein:

the laser subsystem comprises an IR laser.

The laser-machining system of paragraph 126, wherein:

the laser subsystem is adapted to provide a laser beam including IR and UV wavelengths.

The laser-machining system of paragraph 126, wherein:

the control subsystem provides focus control signals to the optical subsystem in response to the image data; and

the optic subsystem is adapted to change the focus depth of the laser beam in response to the focus control signals.

The laser-machining system of paragraph 126, wherein the control system is adapted to analyze the image data and verify that the tissue retainer is within design tolerances for the selected configuration.

The laser-machining system of paragraph 126, further comprising a stabilization device adapted to stabilize the suture thread adjacent the selected location.

The laser-machining system of paragraph 126, further comprising a stabilization device adapted to stabilize the suture thread adjacent the selected location without mechanical contact with the suture thread.

The laser-machining system of paragraph 126, further comprising a fluid bearing adapted to stabilize the suture thread adjacent the selected location.

The laser-machining system of paragraph 126, further comprising an air bearing device which provides a high speed laminar flow of fluid along and surrounding the suture thread at the selected location.

The laser-machining system of paragraph 126, wherein:

the optic subsystem includes one or more axicon prisms.

The laser-machining system of paragraph 126, wherein:

the laser beam has a Gaussian power density distribution.

The laser-machining system of paragraph 126, wherein:

the laser beam has a ring-shaped power density distribution of selectable ring diameter.

A stabilization device for contactless stabilization of a suture thread in a region of the suture thread, wherein the stabilization device comprises:

a source of pressurized fluid; and

a fluid outlet connected to the source of pressurized fluid and adapted to generate a laminar flow of fluid along the suture thread and surrounding the suture thread in the region of the suture thread.

The stabilization device of paragraph 140, wherein:

the fluid outlet is nozzle-shaped.

The stabilization device of paragraph 140, wherein:

the suture thread passes through the fluid outlet.

The stabilization device of paragraph 140, wherein the stabilization device comprises:

a fluid manifold wherein the fluid manifold is connected to the source of pressurized fluid and the fluid outlet is connected to one end of the fluid manifold;

a suture inlet connected to the fluid manifold; and

wherein the stabilization device is configured such that a suture thread can enter the fluid manifold through an entry port and leave the fluid manifold through the fluid outlet without contacting the entry port and fluid outlet.

The stabilization device of paragraph 140 in combination with a machining system adapted to direct a laser beam at the suture thread to create a tissue retainer in the region of the suture thread.

The stabilization device of paragraph 140, in combination with a laser-machining system comprising:

a laser subsystem adapted to provide a laser beam,

an optic system adapted to receive the laser beam and generate a focused laser beam directed at a volume of the suture thread,

a transport subsystem adapted to move the suture thread relative to the laser beam,

an imaging subsystem adapted to image the suture thread and generate image data; and

a control subsystem adapted to control the laser subsystem and transport subsystem to create a tissue retainer of a selected configuration in the region of the suture thread.

A method for creating a self-retaining suture comprising:

-   (a) positioning a selected region of the suture thread in a laminar     flow of fluid adapted to stabilize the position of the selected     region of the suture thread; -   (b) directing a laser beam at a selected volume of suture material     within the selected region of the suture thread; -   (c) removing the selected volume of the suture material from within     the selected region of the suture thread to create a tissue     retainer; -   (d) repeating steps (a), (b) and (c) for a plurality of selected     regions of the suture thread to create a plurality of tissue     retainers.

The method of paragraph 146, further comprising:

-   (e) positioning a selected marking region of the suture thread in     the laminar flow of fluid and directing electromagnetic radiation at     the suture thread within the selected marking region wherein the     electromagnetic radiation is adapted to change a visual     characteristic of the selected marking region of the suture thread     without ablating suture material.

A laser-machining system adapted to make tissue retainers on a suture thread, wherein the laser-machining system comprises:

a laser subsystem adapted to provide a laser beam;

an optic system adapted to receive the laser beam and generate a focused laser beam directed at a volume of the suture thread;

a transport subsystem adapted to move the suture thread relative to the focused laser beam;

a marking subsystem adapted to change a visual characteristic of a selected region of the suture thread without ablating suture material; and

a control subsystem adapted to control the laser subsystem, marking subsystem, and transport subsystem to create a tissue retainer of a selected configuration at a selected location on said suture thread and create a visible marker on the suture thread at a different selected location on said suture thread.

A method for making a self-retaining suture comprising;

-   (a) identifying a tissue retainer location on the suture thread; -   (b) providing a laser beam; -   (b) directing a laser beam at a portion of the tissue retainer     location on the suture thread; -   (c) using the laser beam to remove a volume of suture material from     the tissue retainer location on the suture thread to create a tissue     retainer having a tip; -   (d) repeating steps (a), (b) and (c) to generate a plurality of     tissue retainers on the suture thread; and -   (e) subsequent to step (d) treating the self-retaining suture to     elevate the tips of the plurality of tissue retainers so that the     tips protrude from the suture thread.

The method of paragraph 149, further comprising:

-   (f) subsequent to step (e) annealing the self-retaining suture to     maintain the tips of the plurality of tissue retainers so that the     tips protrude from the suture thread.

The method of paragraph 149, wherein step (e) comprises treating the self-retaining suture with heat to elevate the tips of the plurality of tissue retainers so that the tips protrude from the suture thread.

The method of paragraph 149, wherein step (e) comprises treating the self-retaining suture with tension to elevate the tips of the plurality of tissue retainers so that the tips protrude from the suture thread.

The method of paragraph 149, wherein step (e) comprises treating the self-retaining suture with heat and tension to elevate the tips of the plurality of tissue retainers so that the tips protrude from the suture thread.

A method for making a self-retaining suture comprising;

-   (a) providing a suture thread having a surface; -   (b) identifying a first volume of suture material on the surface of     the thread; -   (c) identifying a second volume of suture material from within the     first volume of suture material; -   (d) directing a laser beam at the suture thread to ablate all of the     suture material within the first volume of suture material with the     exception of the second volume of suture material whereby the second     volume of suture material forms a tissue retainer protruding from     laser cut surface of the suture thread; and -   (e) repeating steps (b), (c) and (d) to generate a plurality of     tissue retainers protruding from the suture thread.

The method of paragraph 154, wherein step (c) comprises identifying a second volume of suture material from within the first volume of suture material the second volume being less than 50% of the first volume.

The method of paragraph 154, wherein step (c) comprises identifying a second volume of suture material from within the first volume of suture material the second volume being less than 25% of the first volume.

The method of paragraph 154, wherein:

step (c) comprises identifying a conical subvolume of suture material from within the volume of suture material wherein the subvolume of suture material; and

step (d) comprises directing a laser beam at the suture thread to ablate all of the suture material within the selected volume of suture material with the exception of the conical subvolume of suture material whereby the conical subvolume of suture material forms a tissue retainer protruding from laser cut surface of the suture thread.

The method of paragraph 154, wherein step (a) comprises providing a suture thread having a surface and a noncircular cross-section.

The method of paragraph 154, wherein:

step (a) comprises providing a suture thread having a surface and a plurality of longitudinal ridges noncircular cross-section; and

step (b) comprises identifying a first volume of suture material on the surface of the thread within one of the longitudinal ridges.

The method of paragraph 154, wherein:

step (a) comprises providing a suture thread having a surface and a polygonal cross section having a plurality of longitudinal apices; and

step (b) comprises identifying a first volume of suture material on the surface of the thread including one of the longitudinal apices.

Although the present invention has been shown and described in detail with regard to only a few exemplary embodiments of the invention, it should be understood by those skilled in the art that it is not intended to limit the invention to the specific embodiments disclosed. Various modifications, omissions, and additions may be made to the disclosed embodiments without materially departing from the novel teachings and advantages of the invention, particularly in light of the foregoing teachings. Accordingly, it is intended to cover all such modifications, omissions, additions, and equivalents as may be included within the spirit and scope of the invention as defined by the following claims. 

What is claimed is:
 1. A method for making a self-retaining suture comprising; (a) providing a suture thread having a surface; (b) identifying a first volume of suture material on the surface of the thread; (c) identifying a second volume of suture material from within the first volume of suture material; (d) directing a laser beam at the suture thread to ablate all of the suture material within the first volume of suture material with the exception of the second volume of suture material whereby the second volume of suture material forms a tissue retainer protruding from laser cut surface of the suture thread; and (e) repeating steps (b), (c) and (d) to generate a plurality of tissue retainers protruding from the suture thread.
 2. The method of claim 1, wherein step (c) comprises identifying a second volume of suture material from within the first volume of suture material the second volume being less than 50% of the first volume.
 3. The method of claim 1, wherein step (c) comprises identifying a second volume of suture material from within the first volume of suture material the second volume being less than 25% of the first volume.
 4. The method of claim 1, wherein: step (c) comprises identifying a conical subvolume of suture material from within the volume of suture material wherein the subvolume of suture material; and step (d) comprises directing a laser beam at the suture thread to ablate all of the suture material within the selected volume of suture material with the exception of the conical subvolume of suture material whereby the conical subvolume of suture material forms a tissue retainer protruding from laser cut surface of the suture thread.
 5. The method of claim 1, wherein step (a) comprises providing a suture thread having a surface and a noncircular cross-section.
 6. The method of claim 1, wherein: step (a) comprises providing a suture thread having a surface and a plurality of longitudinal ridges noncircular cross-section; and step (b) comprises identifying a first volume of suture material on the surface of the thread within one of the longitudinal ridges.
 7. The method of claim 1, wherein: step (a) comprises providing a suture thread having a surface and a polygonal cross section having a plurality of longitudinal apices; and step (b) comprises identifying a first volume of suture material on the surface of the thread including one of the longitudinal apices.
 8. A method for making a self-retaining suture comprising; (a) identifying a tissue retainer location on the suture thread; (b) directing a laser beam at the tissue retainer location on the suture thread; (c) using the laser beam to remove a volume of material defining a slot from said suture thread, wherein the slot defines a tissue engagement surface of a tissue retainer; (d) repeating steps (a), (b) and (c) to generate a plurality of tissue retainers on the suture thread.
 9. The method of claim 8, wherein step (c) comprises (c1) using the laser beam to remove a volume of material defining a slot from said suture thread, wherein the slot defines a tissue engagement surface of a tissue retainer; and (c2) using the laser beam to remove a wedge-shaped volume of material from said suture thread adjacent the slot to provide an entrance ramp which promotes engagement of tissue by said tissue engagement surface.
 10. The method of claim 8, wherein step (b) comprises directing a laser beam at the tissue retainer location on the suture thread and focusing the laser beam to a diameter no greater than 5 nm.
 11. The method of claim 8, wherein step (b) comprises directing a femtosecond laser beam at the tissue retainer location on the suture thread.
 12. The method of claim 8, further comprising: (e) after completion of step (d), treating the suture thread to cause a tip of each of said plurality of retainers to elevate above a surface of said suture thread.
 13. The method of claim 8, further comprising: (e) after completion of step (d) treating the suture thread to cause a tip of each of said plurality of retainers to elevate above a surface of said suture thread; and (f) annealing the suture thread to cause a tip of each of said plurality of retainers to remain elevated above the surface of said suture thread.
 14. A laser-machining system adapted to make tissue retainers on a suture thread, wherein the laser-machining system comprises: a laser subsystem adapted to provide a laser beam; an optic system adapted to receive the laser beam and generate a focused laser beam directed at a volume of the suture thread; a transport subsystem adapted to move the suture thread relative to the laser beam; an imaging subsystem adapted to image the suture thread and generate image data; and a control subsystem adapted to receive said image data from the laser subsystem and transport subsystem to create a tissue retainer of a selected configuration at a selected location on said suture thread.
 15. The laser-machining system of claim 14, wherein: the laser subsystem comprises a femtosecond laser.
 16. The laser-machining system of claim 14, wherein: the control subsystem provides focus control signals to the optical subsystem in response to the image data; and the optic subsystem is adapted to change the focus depth of the laser beam in response to the focus control signals.
 17. The laser-machining system of claim 14 further comprising an air bearing device which provides a high speed laminar flow of fluid along and surrounding the suture thread at the selected location.
 18. The laser-machining system of claim 14, wherein; the optic subsystem includes one or more axicon prisms.
 19. The laser-machining system of claim 14, wherein: the laser beam has a ring-shaped power density distribution of selectable ring diameter.
 20. A stabilization device for contactless stabilization of a suture thread in a region of the suture thread, wherein the stabilization device comprises: a source of pressurized fluid; and a fluid outlet connected to the source of pressurized fluid and adapted to generate a laminar flow of fluid along the suture thread and surrounding the suture thread in the region of the suture thread.
 21. The stabilization device of claim 20, wherein the stabilization device comprises: a fluid manifold wherein the fluid manifold is connected to the source of pressurized fluid and the fluid outlet is connected to one end of the fluid manifold; a suture inlet connected to the fluid manifold; and wherein the stabilization device is configured such that a suture thread can enter the fluid manifold through an entry port and leave the fluid manifold through the fluid outlet without contacting the entry port and fluid outlet.
 22. A method for creating a self-retaining suture comprising: (a) positioning a selected region of the suture thread in a laminar flow of fluid adapted to stabilize the position of the selected region of the suture thread; (b) directing a laser beam at a selected volume of suture material within the selected region of the suture thread; (c) removing the selected volume of the suture material from within the selected region of the suture thread to create a tissue retainer; (d) repeating steps (a), (b) and (c) for a plurality of selected regions of the suture thread to create a plurality of tissue retainers.
 23. The method of claim 22, further comprising: (e) positioning a selected marking region of the suture thread in the laminar flow of fluid and directing electromagnetic radiation at the suture thread within the selected marking region wherein the electromagnetic radiation is adapted to change a visual characteristic of the selected marking region of the suture thread without ablating suture material.
 24. A method for making a self-retaining suture comprising; (a) identifying a tissue retainer location on the suture thread; (b) providing a laser beam; (b) directing a laser beam at a portion of the tissue retainer location on the suture thread; (c) using the laser beam to remove a volume of suture material from the tissue retainer location on the suture thread to create a tissue retainer having a tip; (d) repeating steps (a), (b) and (c) to generate a plurality of tissue retainers on the suture thread; and (e) subsequent to step (d) treating the self-retaining suture to elevate the tips of the plurality of tissue retainers so that the tips protrude from the suture thread.
 25. The method of claim 24, further comprising: (f) subsequent to step (e) annealing the self-retaining suture to maintain the tips of the plurality of tissue retainers so that the tips protrude from the suture thread. 